Elevator sheave for use with flat ropes

ABSTRACT

In an elevator sheave for a flat belt, the optimum crown height is within a range of approximately 0.033 to about 0.003 times the width of the elevator rope. The optimum radius is in the range of about 16.67 to about 50.00 times the width of the elevator rope. Both the crown height (h) and the crown radius (rc) may be expressed as a function of belt width (Wb). The groove width (wg) is in the range of approximately 1.5 and 2.25 times the width of the belt (Wb). A circumferential surface roughness of about 1.0 to 3.0 is applied. A hard, thin surface coating can be applied to enhance durability while maintaining traction.

TECHNICAL FIELD

The present invention relates to elevators and, more particularly, to anovel sheave design for improved performance and durability.

BACKGROUND AND SUMMARY OF THE INVENTION

Conventional elevator systems have long utilized standard elevator ropesto suspend and move elevator cars. In order to optimize performance insuch areas as traction, durability, ride quality and safety, numerousdesign parameters have limited various components such as motors,sheaves and rope grade to certain sizes, weights and dimensions.

New generation elevator systems are being developed that eliminate theneed for various conventional components, through the implementation ofsuperior performing traction and drive systems and other advancements.These types of systems offer many advantages over traditional elevatorsystems, including structural versatility and economy, convenient accessfor servicing and repair, and lighter building loads.

One particular advancement is the implementation of high-traction, highdurability elevator ropes that are smooth running, light in weight andcorrosive-resistant. One such type of rope is made of a plurality oftension-carrying cord members contained in a unitary insulation jacketmade of, for example, a urethane material. For optimum performance withsuch ropes, it is desirable to adapt various components such as sheavesto interface closely.

Conventional elevator sheaves are cast iron and designed to accommodatetraditional round, steel wire ropes. With the increasing feasibility ofnew generation elevator ropes, such as elastomer-coated, flat ropes, newproblems related to tracking, traction and durability must be addressed.It is an object of the present invention to provide a sheave designhaving particular dimensional, geometric, and surface characteristicsselected for optimum performance and durability for use with such newgeneration elevator ropes.

This object and others are achieved by the present invention sheavedesign. The present invention sheave design provides a convex contactsurface defined by a crown height and crown radius dimension related torope or belt width for tracking. Another aspect of the invention relatesto a sheave design in which sheave groove width is related to belt widthfor tracking. Another aspect of the invention relates to providing aparticular circumferential roughness to the contact surface fortraction. The circumferential surface roughness is preferably about 1.0to about 3.0 microns. Yet another aspect of the invention relates toproviding a hard, corrossion-resistant coating on the sheave contactsurface for improved durability. The coating preferably has a thicknessof about 1-2 microns. The coating preferably has a hardness of greaterthan about 40 HRC.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic side view of a multi-rope sheave according to thepresent invention.

FIG. 2 is a schematic, partial view of the contact surfaces of amulti-rope sheave according to FIG. 1.

FIG. 3 is a schematic view of an elevator system according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An elevator system (20) is illustrated in FIG. 3. The system (20)includes an elevator car (22) suspended by ropes (24) having fixed ends(26, 28) that are fixed with respect to a hoistway (not shown). Acounterweight (30) is also suspended by the ropes (24) and coupled tothe elevator car (22) for relative movement therewith. The elevator caris suspended from the ropes (24) by car idler sheaves (32, 34) and thecounterweight is suspended from the ropes (24) by a counterweight idlersheave (36). A drive machine (38) having a traction sheave (40) forengaging and driving the ropes (24 is provided in a fixed relationshipwith respect to the hoistway.

A multiple-rope elevator sheave (10), illustrated in FIG. 1, is adaptedto engage elevator ropes (24) to provide traction and support thereto inan elevator assembly (20). Referring to FIGS. 1-2, the sheave (10)comprises a plurality of convex contact surfaces (12, 14, 16) adapted toengage friction surfaces of elevator ropes or belts (18). Each contactsurface (12, 14, 16) is characterized by groove width (wg), crown height(h), and crown radius (rc). Flat rope or belt tracking is controlled bya crown height (h) or crown radius (rc) groove width (wg). In contrastto flat contact surfaces on sheaves, the convex surfaces (12, 14, 16)provide contour-conforming fit when used with a flat, flexible rope(18). With the use of such convex contact surfaces and flat, flexibleropes, configured in accordance with the present invention, it is notnecessary to provide dividers between contact surfaces to maintain ropeor belt tracking.

For a belt (18)having a width (Wb) of 30 mm, the optimum crown height(h) has been determined to be within a range of approximately 0.1 mm to1.0 mm. The optimum radius (rc) is in the range of approximately 500 mmto 1500 mm. Both the crown height (h) and the crown radius (rc) may beexpressed as a function of belt width (Wb). In the preferred embodiment,the crown height (h) is in the range of approximately 0.3 to 3.0 percentof the belt width (Wb). The crown radius (rc) is preferably in the rangeof approximately 15 to 50 times the belt width (Wb).

The groove width (wg) is in the range of approximately 1.5 and 2.25times the width of the belt (Wb). This groove width accommodatesmisalignments that may result from installation or from movement of theelevator car and counterweight. Also, the selection of steering anglesfor car-mounted sheaves may result in misalignments. Car-mountedsheaves, in contrast to the traction sheave and thecounterweight-mounted sheave, have two steering angles—vertical andhorizontal. The ideal setting for one angle may result in a less thanoptimum setting for the other. With proper selection of groove height(h) and width (wg), sufficient tracking may be achieved such thatdividers ordinarily required between adjacent sheave grooves may beeliminated.

Traction of the traction sheave is now enhanced by providingcircumferential roughness to the contact surfaces of the tractionsheave. Conventional sheaves are machined in a manner that results intransverse roughness on the contact surface. This type of roughness doesnot enhance traction. Circumferential roughness provides good tractioneven in the presence of contaminants on the contact surface. Thepreferred range of circumferential roughness is approximately 1.0 to 3.0microns. The preferred method of forming the circumferential roughnessis shot peening. Grit blasting may also be used, but it provides morejagged surface texture than shot peening, thereby increasing the rate ofbelt wear.

Durability of the sheave is enhanced by applying a corrosion-resistantcoating to the contact surface of the sheaves. The coating is a thinlayer, less than 10 microns thick, and preferably 1-2 microns thick. Thecircumferential roughness of 1-3 microns should be present after theapplication of the coating to the sheave. Using a thin layer of coatingpermits the surface roughness and the crowning of the substrate to bemaintained. The surface morphology of the coating should have anirregular or nodular nature without any sharp cutting features whichmight damage the surface of the rope. A hard coating is selected havinga hardness of greater than 40 HRC. The thin layer of coating permits thesurface roughness and the crowning to be maintained. Without thecoating, the contact surfaces of the sheave would get worn smooth. Thesurfaces of the sheave would get worn smooth. The surface morphology ofthe coating should have an irregular or nodular nature without any sharpcutting features that might damage the surface of the flat rope. Thecoating is corrosion resistant to enhance the sheaves which arepreferably made of steel, rather than conventional cast iron. Thecoating should be a low temperature coating, such as about 25-80° C., sothat it can be applied to the sheave in the finished state. The coatingmay be applied, for example, by a dip process or an electromechanicalprocess.

For idler sheaves, a low friction coating may be applied to the sheaveor the sheave may be formed from a material that exhibits theseproperties, such as polyurethane. Because the traction is less importantfor idler sheaves, surface roughness is not essential.

While the preferred embodiments have been herein described, it isunderstood and acknowledged that modification and variation can be madewithout departing from the scope of the presently claimed invention.

What is claimed is:
 1. A traction sheave for engaging an elevator rope,the traction sheave comprising: a traction surface for engaging anddriving the elevator rope, the traction surface having a circumferentialsurface roughness in a range of approximately 1.0 to approximately 3.0microns.
 2. The traction sheave according to claim 1, wherein thetraction surface has a hardness of greater than approximately 40 HRC. 3.The traction sheave according to claim 1, wherein the traction surfacecomprises a corrosion-resistant surface coating.
 4. A traction sheaveaccording to claim 1, wherein the traction surface comprises acorrosion-resistant surface coating having a thickness of less than 10microns.
 5. The traction sheave according to claim 4, wherein thesurface coating thickness is in a range of approximately 1 micron toapproximately 2 microns.
 6. The traction sheave according to claim 5,wherein the surface coating surface has a hardness of greater thanapproximately 40 HRC.
 7. A traction sheave for engaging an elevatorrope, the traction sheave comprising: a traction surface for engagingand driving the elevator rope, the traction surface being formed from acorrosion-resistant material, wherein the corrosion-resistant materialcomprises a surface coating having a thickness of less than 10 microns.8. The traction sheave according to claim 7, wherein the surface coatingthickness is in a range of approximately 1 micron to approximately 2microns.
 9. The traction sheave according to claim 8, wherein thesurface coating has a hardness of greater than approximately 40 HRC. 10.A traction sheave for engaging an elevator rope, the traction sheavecomprising: a traction surface for engaging and driving the elevatorrope, the traction surface being formed from a corrosion-resistantmaterial, wherein the traction surface has a hardness of greater thanapproximately 40 HRC.
 11. A traction sheave for engaging an elevatorrope, the traction sheave comprising: a traction surface for engagingand driving the elevator rope, the traction surface being formed from acorrosion-resistant material, wherein the traction surface has acircumferential surface roughness of approximately 1.0 to approximately3.0 microns.
 12. A traction sheave for engaging an elevator rope, thetraction sheave comprising: a traction surface for engaging and drivingthe elevator rope; and a surface coating applied to the tractionsurface, wherein the coating has a hardness of greater thanapproximately 40 HRC.
 13. The traction sheave according to claim 12,wherein the traction surface has a circumferential surface roughness ofapproximately 1.0 to approximately 3.0 microns.
 14. The traction sheaveaccording to claim 13, wherein the surface coating has a thickness ofless than 10 microns.
 15. A traction sheave for engaging an elevatorrope, the traction sheave comprising: a traction surface for engagingand driving the elevator rope; and a corrosion-resistant surface coatingapplied to the traction surface and having a thickness of less than 10microns.
 16. The traction sheave according to claim 15, wherein thesurface coating exhibits a circumferential roughness of approximately1.0 to approximately 3.0 microns.
 17. The traction sheave according toclaim 15, wherein the surface coating has a hardness of greater thanapproximately 40 HRC.
 18. The traction sheave according to claim 17,wherein the traction surface has a circumferential roughness ofapproximately 1.0 to approximately 3.0 microns.